Bearing structure for cooling fan

ABSTRACT

A cooling fan includes a fan housing ( 50 ) having a central tube ( 52 ), a bearing structure received in the central tube, a stator ( 60 ) mounted around the central tube, and a fan blade set ( 70 ). The bearing structure includes a shaft ( 30 ) being rotatably received in the central tube and connecting to the fan blade set. An inner bearing ( 20 ) is fixedly mounted around the shaft to rotate with the shaft. Upper and lower outer bearings ( 10 ) are fixedly mounted into the central tube and are mounted around two opposite ends of the inner bearing, respectively. The inner and outer bearings are made of magnetic materials. The inner bearing floats between the outer bearings whereby rotation of the shaft does not cause the inner and outer bearings to wear.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cooling fan, and more particularly relates to a cooling fan having an improved bearing structure.

2. Description of Related Art

With the continuing development of the electronic technology, electronic packages such as CPUs (central processing units) are generating more and more heat that requires immediate dissipation. Cooling fans are commonly used in combination with heat sinks for cooling CPUs.

Oftentimes, a cooling fan includes a blade set and a fan seat. The fan seat has a central tube portion integrally formed thereon. A sleeve bearing is arranged in the tube portion. A coil is wound around an outside of the tube portion. The fan blade set is formed with a cap and a plurality of fan blades connecting to the cap. A rotary shaft made of stainless steel, which is extended downwardly from the cap is rotatably supported by the sleeve bearing. A magnet pushed by magnetic force of the coil is fixed to the cap and is driven by the coil to rotate so that the fan blades can produce an airflow. Since the aforesaid rotary shaft is arranged to rotate in the sleeve bearing, after rotating for a period of time, the rotary shaft and the bearings will experience wear due to leakage of lubricating oil contained therebetween. Thus, the lifetime of the fan will be reduced. In order to improve the lifetime of the fan, a ball bearing, which has a point contact with the rotary shaft has been developed. By the point contact, the rotary shaft and the ball bearing can have little wear even after a long period of use thereof. However, the manufacturing process for the ball bearings requires a precise grinding and a high-degree polish; thus, the ball bearings and the cooling fans incorporating the ball bearings are expensive.

For the foregoing reasons, therefore, there is a need in the art for a cooling fan which overcomes the above-mentioned problems.

SUMMARY OF THE INVENTION

According to a preferred embodiment of the present invention, a cooling fan includes a fan housing having a central tube extending upwardly, a bearing structure received in the central tube, a stator mounted around the central tube, and a fan blade set. The bearing structure includes a shaft being rotatably received in the central tube and connecting to the fan blade set. An inner bearing is fixedly mounted around the shaft to rotate with the shaft. A pair of outer bearings are fixedly mounted into the central tube and are mounted around two opposite ends of the inner bearing, respectively. The inner and outer bearings are made of magnetic materials, wherein the outer bearings exert repelling forces on the inner bearing to make the inner bearing always be spaced from the outer bearings.

Other advantages and novel features of the present invention will be drawn from the following detailed description of the preferred embodiments of the present invention with attached drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present bearing structure for cooling fan can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present bearing structure for cooling fan. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 is an isometric, assembled view of a bearing structure in accordance with a preferred embodiment of the present invention;

FIG. 2 is a cross-sectional view of the bearing structure of FIG. 1;

FIG. 3 is similar to FIG. 2, but shows an alternative embodiment of the bearing structure according to the present invention; and

FIG. 4 is cross-sectional view of a cooling fan incorporating the bearing structure in accordance with a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 and 2, a bearing structure according to a preferred embodiment of the present invention is shown. The bearing structure includes a rotary shaft 30, an inner bearing 20, and a pair of outer bearings 10.

The shaft 30 is column-shaped. The inner bearing 20 is fixedly mounted around the shaft 30 to rotate with the shaft 30. The inner bearing 20 is cylindrical-shaped, with an inner diameter of the inner bearing 20 being approximately the same as a diameter of the shaft 30. An outer surface 220, 240 of each end (i.e., top and bottom ends 22, 24) of the inner bearing 20 has an arc-shaped configuration. An outer diameter of each end 22, 24 of the inner bearing 20 is gradually decreased toward top and bottom extremities (not labeled) thereof, wherein the top and bottom extremities of the inner bearing 20 each have a diameter about the same as that of the shaft 30. In this embodiment, an outer diameter of the inner bearing 20 is approximately the same as a height of each end 22, 24 of the inner bearing 20, and thus each end 22, 24 of the inner bearing 20 has a shape of a hemispheroid. The inner bearing 20 can be assembled to the shaft 30 by insert molding the inner bearing 20 to the shaft 30. In the insert molding, firstly, the shaft 30 is mounted in a mold which is used for making the inner bearing 20. The mold has a chamber for injecting molten magnetic material thereinto. The molten magnetic material is then injected into the chamber of the mold. After cooling, the molten magnetic material in the chambersolidifies to form the inner bearing 20. The inner bearing 20 is integrally formed with the shaft 30, and is fixedly secured to the outer surface of the shaft 30. Alternatively, the shaft 30 and the inner bearing 20 can be formed separately, and then connected together by interferential fitting or adhering.

The outer bearings 10 are respectively mounted around the top and bottom ends 22, 24 of the inner bearing 20. Each of the outer bearings 10 is bowl-shaped. A hemispheroidal-shaped inner space 13 is defined in each outer bearing 10. Each outer bearing 10 defines a through hole 11 in an outer end thereof. The through hole 11 communicates with the inner space 13. A diameter of the through hole 11 is larger than that of the shaft 30, and a diameter of the inner space 13 of the outer bearing 10 is larger than the outer diameter of the inner bearing 20. When the inner and outer bearings 20, 10 are assembled together, the pair of outer bearings 10 are respectively arranged around the top and bottom ends 22, 24 of the inner bearing 20. A narrow gap is defined between each end 22, 24 of the inner bearing 20 and a corresponding outer bearing 10. A width of the gap at the top end 22 of the inner bearing 20 is about d1, and a width of the gap at the bottom end 24 of the inner bearing 20 is about d2. Top and bottom ends of the shaft 30 extend through the through holes 11 of the outer bearings 10, respectively, for connecting with a load to bear the load thereon. The inner and outer bearings 20, 10 are magnetized. An inner side of each outer bearing 10 has a polarity similar to that of a corresponding end 22, 24 of the inner bearing 20. In this embodiment, the top end 22 of the inner bearing 20 is S (south pole), and the bottom end 24 of the inner bearing 20 is N (north pole). The inner side of the upper outer bearing 10 is S, and an outer side of the upper outer bearing 10 is N. Conversely, the inner side of the lower outer bearing 10 is N, and an outer side of the lower outer bearing 10 is S.

During operation of the bearing structure, a repelling force is generated between each end 22, 24 of the inner bearing 20 and the corresponding outer bearing 10. As the upper outer bearing 10 is mounted around the top end 22 of the inner bearing 20 and is approximately symmetric to an axis of the inner bearing 20, the resultant force acting on the top end 22 of the inner bearing 20 by the upper outer bearing 10 along the latitudinal direction is zero, and the resultant force acting on the top end 22 of the inner bearing 20 by the upper outer bearing 10 along the longitudinal direction is downward. Similarly, the resultant force acting on the bottom end 24 of the inner bearing 20 by the lower outer bearing 10 along the latitudinal direction is zero, and the resultant force acting on the bottom end 24 of the inner bearing 20 by the lower outer bearing 10 along the longitudinal direction is upward. The forces acting on the top and bottom ends of the inner bearing 20 by the upper and lower outer bearings 10 have opposite directions, wherein the force acting on the bottom end of the inner bearing 20 has an amount which is equal to that of the force acting on the top end of the inner bearing 20 plus the weight of the inner bearing 20 and the shaft 30. In other words, the resultant force acting on the shaft 30 is zero, and thus the shaft 30 is in a balanced state and the inner bearing 20 is spaced from and floats between the outer bearings 10. As the shaft 30 is supported by the repelling magnetic force established between the inner and outer bearings 20, 10, and the inner and outer bearings 20, 10 are spaced from each other, friction between the inner and outer bearings 20, 10 is avoided. Thus, the rotation of the shaft 30 does not cause the outer bearings 10, the inner bearing 20 and the shaft 30 to wear, and a life span of the bearing structure can be extended.

On the other hand, if an outside force Pn, as shown in FIG. 2, which acts downwardly, is exerted on a top end of the shaft 30, the original balance of the shaft 30 is broken. The shaft 30 moves downwardly. The gap d1 between the top end 22 of the inner bearing 20 and the upper outer bearing 10 increases, whilst the gap d2 between the bottom end 24 of the inner bearing 20 and the lower outer bearing 10 decreases. The magnetic force between the top end 22 of the inner bearing 20 and the upper outer bearing 10 decreases with the increasing gap d1 defined therebetween. The magnetic force between the bottom end 24 of the inner bearing 20 and the lower outer bearing 10 increases with the decreasing gap d2 defined therebetween. Thus, the upwardly resultant force acting on the bottom end 24 of the inner bearing 20 by the lower outer bearing 10 increases, and the downwardly resultant force acting on the top end 22 of the inner bearing 20 by the upper outer bearing 10 decreases. The resultant force acting on the inner bearing 10 and accordingly on the shaft 30 by the outer bearings 10 has an upward direction, motivating the shaft 30 to move upwardly. Thus, the downward movement of the shaft 30 due to the action of the outside force Pn is counteracted by the increased, upward resultant force of the outer bearings 10 acting on the inner bearing 20. Thus the bearing structure enables the shaft 30 to keep in a new balanced state when an outside force is exerted on the shaft 30, if the downward outside force is not larger than the increased, upward resultant force which can be generated by the outer bearings 10.

FIG. 3 shows an alternative embodiment of the bearing structure according to the present invention. The bearing structure includes a shaft 30 a, an inner bearing 20 a being fixedly mounted on the shaft 30 a, and a pair of outer bearing 10 a, 10 b arranged on the top and bottom ends 22 a, 24 a of the inner bearing 20 a, respectively. The gap 13 a is defined between each end 22 a, 24 a of the inner bearing 20 a and the outer bearings 10 a, 10 b. The difference between this embodiment and the previously embodiment is that only the top end 22 a of the inner bearing 20 a is open, and the bottom end 24 a of the inner bearing 20 a is closed and thus receives the bottom end of the shaft 30 therein. The upper outer bearing 10 a defines the through hole 11 a for the top end of the shaft 30 a to extend therethrough. The outer end of the lower outer bearing 10 b is closed corresponding the closed bottom end 24 a of the inner bearing 20 a. Similarly, the inner side of each outer bearing 10 a, 10 b has a polarity similar to that of the corresponding end 22 a, 24 a of the inner bearing 20 a, thereby to establish repelling forces therebetween.

FIG. 4 shows a cooling fan incorporating the bearing structure in accordance with a third embodiment of the present invention. In this embodiment, the bearing structure also includes a shaft 30 c, an inner bearing 20 c being fixedly mounted on the shaft 30 c, and a pair of outer bearing 10 c, 10 d arranged on the top and bottom ends of the inner bearing 20 c, respectively. The difference between this embodiment and the second embodiment is that each outer bearing 10 c, 10 d has a column-like shape with a recessed top face for the lower outer bearing 10 d and a recessed bottom face for the upper outer bearing 10 c. Like the second embodiment, a bowl-shaped inner space 13 c is defined in each outer bearing 10 c, 10 d receiving the corresponding end of the inner bearing 20 therein. The cooling fan has a housing 50 forming a central tube 52 receiving the bearing structure therein. The central tube 52 extends upwardly from a central portion of the housing 50 and defines a central hole 56 therethrough. A plug 80 is inserted to a bottom end of the central hole 56 for sealing the bottom end of the central tube 52. A diameter of the central hole 56 is approximately the same as or a little smaller than the outer diameter of the outer bearings 10 c, 10 d. The bearing structure can be fixedly mounted into the central tube 52 by interferential fitting or adhering. An annular flange 54 extends inwardly from a top end of the central tube 52. The flange 54 has an inner diameter smaller than the outer diameter of the outer bearings 10 c, 10 d and is positioned to abut against a top surface of the upper outer bearing 10 c for limiting movement of the upper outer bearing 10 c.

A stator 60 is mounted around the central tube 52. The stator 60 includes a stator core 603 with coils 602 wound thereon to establish an alternating magnetic field, and a PCB 601 (printed circuit board) with electronic components mounted thereon being electrically connected with the coils 602 to control electrical current flowing through the coils 602. A fan blade set 70 is connected to the top end of the shaft 30 c which extends through the through hole 11 c of the upper outer bearing 10 c to rotate with the inner bearing 20 c. The fan blade set 70 includes a hub 72, a plurality of fan blades 74 extending radially and outwardly from an outer periphery of the hub 72, and a magnet 76 adhered to an inner side of the hub 72 and confronting the coils 602 of the stator 60. During operation, the fan blade set 70 is driven to rotate by the interaction of the alternating magnetic field established by the stator 50 and the magnetic field of the magnet 76. Rotation of the fan blades 74 generates forced airflow for heat exchange with a heat generating component (not shown). As the shaft 30 c and the inner bearing 20 c are fixedly connected to the fan blade set 70, the shaft 30 c and the inner bearing 20 c rotate with the fan blade set 70. Due to the support of the bearing structure, rotation of the shaft 30 c is smooth and stable. Furthermore, the inner bearing 20 c can be assembled to the shaft 30 c during process of insert molding the inner bearing 20 c. Thus the inner bearing 20 c and the shaft 30 c can be assembled precisely and easily, thereby achieving a relatively low cost and a relatively high performance at the same time. By the bearing structure in accordance with the present invention, the life-span of the cooling fan can be prolonged and the cost of the cooling fan can be reduced.

It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

1. A cooling fan comprising: a fan housing having a central tube extending upwardly, the central tube defining a central hole therein; a bearing structure comprising a shaft being rotatably received in the central hole of the central tube, an inner bearing being fixedly mounted around the shaft to rotate with the shaft, and a pair of outer bearings being fixedly mounted into the central tube and being mounted around two opposite upper and lower ends of the inner bearing, respectively, the inner and outer bearings being made of magnetic materials; a stator mounted around the central tube; and a fan blade set being connected with the shaft to rotate with the shaft to generate forced airflow.
 2. The cooling fan of claim 1, wherein an annular flange extends inwardly from a top of the central tube and is located over an upper one of the outer bearings for limiting movement of the upper outer bearing along an axial direction thereof.
 3. The cooling fan of claim 2, wherein the central hole extends through the central tube, a plug being coupled to a bottom of the central hole to seal the bottom of the central tube.
 4. The cooling fan of claim 1, wherein each outer bearing defines an inner space therein, the two opposite upper and lower ends of the inner bearing being respectively received in the inner spaces of the outer bearings, each outer bearing and a corresponding end of the inner bearing defining a gap therebetween.
 5. The cooling fan of claim 4, wherein the inner space is bowl-shaped, and an outer surface of each end of the inner bearing is arc-shaped.
 6. The cooling fan of claim 4, wherein the inner space is hemispheroidal-shaped, and an outer surface of each end of the inner bearing is hemispheroidal-shaped.
 7. The cooling fan of claim 1, wherein an outer surface of each outer bearing has one of the following shapes: bowl, hemispheroid and column.
 8. The cooling fan of claim 1, wherein two opposite ends of the shaft extend through the two opposite upper and lower ends of the inner bearing and the two outer bearings, and each outer bearing defines a through hole with a diameter larger than that of the shaft for extension of the shaft therethrough.
 9. The cooling fan of claim 1, wherein a top end of the shaft extends through the inner bearing and an upper one of the outer bearings arranged on the upper end of the inner bearing and connects to the fan blade set, a bottom end of the shaft being received within the inner bearing.
 10. The cooling fan of claim 1, wherein each end of the inner bearing and a side of a corresponding outer bearing facing to each other have same polarity, thereby generating repelling magnetic forces therebetween.
 11. A bearing structure, comprising: a shaft; an inner bearing being fixedly mounted around the shaft to rotate with the shaft; and a pair of outer bearings being mounted around two opposite ends of the inner bearing, respectively; wherein the inner and outer bearings are made of magnetic materials, each end of the inner bearing and a side of a corresponding outer bearing facing to each other having same polarity, thus generating a repelling magnetic force therebetween.
 12. The bearing structure of claim 11, wherein each of the outer bearings defines an inner space therein, the two opposite ends of the inner bearing being respectively received in the inner spaces of the outer bearings, each end of the inner bearing and the corresponding outer bearing defining a gap therebetween.
 13. The bearing structure of claim 12, wherein the inner space and an outer surface of each end of the inner bearing each are one of bowl-shaped and hemispheroidal-shaped, and an outer surface of each outer bearing has one of the following shapes: bowl, hemispheroid and column.
 14. The bearing structure of claim 11, wherein two opposite ends of the shaft extend through the two ends of the inner bearing and the two outer bearings, and each outer bearing defines a through hole with a diameter larger than that of the shaft for extension of the shaft therethrough.
 15. The bearing structure of claim 11, wherein a top end of the shaft extends through the inner bearing and one of the outer bearings arranged on a top end of the inner bearing, a bottom end of the shaft being received within the inner bearing. 